The present invention relates to a high purity copper-cobalt alloy sputtering target capable of inhibiting the generation of particles. When the component composition is indicated as “%” in the present specification, all such component compositions shall mean “at %” even when there is no particular indication.
Conventionally, while an Al alloy (specific resistance of roughly 3.0 μΩ·cm) has been used as the wiring material of semiconductor devices, pursuant to the miniaturization of wirings, a copper wiring with lower resistance (specific resistance of roughly 2.0 μΩ·cm) has been put into practical application. As the process for forming a copper wiring, generally adopted is the method of forming a diffusion barrier layer made from Ta or TaN on a wiring or a wiring groove, and thereafter subjecting copper to sputter deposition. High purity copper of 5N to 6N is normally produced by performing wet or dry purification to electrolytic copper having a purity level of 4N (excluding gas components) as the crude metal, and this has been used as a sputtering target.
As described above, while copper is extremely effective as a wiring for semiconductors, the reliability of copper wirings is deteriorating due to electromigration and formation of stress-induced voids associated with the miniaturization of wirings, and improvement in the copper wiring material itself is now being demanded. A copper-cobalt alloy can be suggested as this kind of material.
When forming a thin film layer by the sputtering method, a copper-cobalt alloy target is required. The production of this target can be generally classified into the following two types of production methods; namely, the sintering method and the melting/casting method. It can be said that this target is preferably produced by the melting/casting method from the perspective of strength, density and production efficiency of the target.
Nevertheless, a copper-cobalt alloy target has an inherent problem; specifically, a problem in that numerous particles are generated during sputtering.
Thus, upon reviewing the conventional technologies, several kinds of copper-cobalt alloy sputtering targets, in which cobalt (Co) is added to copper (Cu), have been proposed.
For example, Patent Document 1 below describes a Cu-based sputtering target for use in forming an electrode film, wherein 2 to 20 at % of one or more types of transition metal elements selected from (Cr, Co, Mo, W, Fe, Nb, V) are contained, and, in a Cu-based matrix, dispersed is a simple substance of each transition metal element that is insoluble in the matrix, or a transition metal element phase as an alloy phase. Nevertheless, since this technology produces the target by powder metallurgy, it is not advisable from the perspective of strength, density and production efficiency of the target.
Moreover, Patent Document 2 below describes a production method of a fine crystal grain copper material for producing a copper material with fine crystal grains by multi-axis forging treatment where a copper material made from high purity copper or low concentration copper alloy is subject to compression forming from different directions, wherein the initial treatment temperature T1 of performing the first pass of compression forming in the multi-axis forging treatment is a temperature in which dynamic recrystallization occurs at least partially in the copper material.
Patent Document 2 further describes providing a fine crystal grain copper material that is produced based on the foregoing production method, and a sputtering target made from such fine crystal grain copper material. While Co is listed as an additive element of the copper material of Patent Document 2, no specific examples are given, and Patent Document 2 fails to provide any description indicating the generation status of particles after the target is processed.
Moreover, Patent Document 3 below describes a Cu-based sputtering target material capable of producing a thin film having low specific resistance, high corrosion resistance, and small non-uniformity of components, wherein the sputtering target material: has a Cu-based matrix as the main phase; contains an element that is insoluble with Cu and indicates a monotectic system or peritectic system phase diagram; and has a second phase, which is primarily made from the foregoing element, that is precipitated in the Cu matrix at an average area ratio of 5% or less. In this sputtering target material, the average diameter of the second phase is 50 μm or less.
While Co is added to this material, since the raw material is powder and the target is not produced by performing HIP treatment to the raw material powder, this technology is not advisable from the perspective of strength, density and production efficiency of the target.
Moreover, Patent Document 4 below describes realizing an alloy (Cu alloy), which has Cu as its main component and of which adhesion with a glass substrate or a silicon film is improved, and providing a wiring material using this Cu alloy. In order to realize the above, Patent Document 4 proposes using, as the wiring material, a Cu alloy made from Cu, and Au and/or Co, wherein the composition ratio of Cu is 80 to 99.5 wt %, and the sum of the composition ratio of Au and the composition ratio of Cu is 0.5 to 20 wt %. Patent Document 4 further describes that, as a result of depositing the foregoing wiring material on a glass substrate or a silicon wafer based on the sputtering method, sufficiently low electrical resistance and strong adhesive strength with the substrate were observed.
Nevertheless, paragraph 0053 of Patent Document 4 only briefly describes the process of producing a sputtering target, and it appears that Patent Document 4 has no interest whatsoever regarding the problem of the generation of particles when the target is processed.
Generally speaking, upon producing a target, a melted and cast copper-cobalt alloy ingot is processed into a target shape of a predetermined dimension, and the surface thereof is machined to produce the sputtering target.
When the smoothness of the target surface is improved, it is possible to suppress the generation of particles during sputtering, and form a thin film with superior evenness (uniformity).
Nevertheless, with a copper-cobalt alloy, there are problems that cannot be resolved only by causing the surface to be smooth, and there is no conventional technology that has developed a target material based on the foregoing perspective.
Patent Document 1: Japanese Patent No. 3710022
Patent Document 2: JP 2010-65252 A
Patent Document 3: JP 2005-220384 A
Patent Document 4: JP 2003-342653 A